linux-kernel - Re: [PATCH 0/20] return f

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Message-ID: <49757750.6010008@suse.de>
Date:	Tue, 20 Jan 2009 15:03:44 +0800
From:	Coly Li <coly.li@...e.de>
To:	Andreas Dilger <adilger@....com>
Cc:	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Roman Zippel <zippel@...ux-m68k.org>,
	"Sergey S. Kostyliov" <rathamahata@...4.ru>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>,
	Bob Copeland <me@...copeland.com>,
	Anders Larsen <al@...rsen.net>, reiserfs-devel@...r.kernel.org,
	Phillip Lougher <phillip@...gher.demon.co.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Evgeniy Dushistov <dushistov@...l.ru>, Jan Kara <jack@...e.cz>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 0/20] return f_fsid for statfs(2)



Andreas Dilger Wrote:
> On Jan 20, 2009  12:30 +0800, Coly Li wrote:
>> Ext[234] is sophisticated to have on-disk uuid record. Most file systems
>> in the patches (except jfs and reiser3) do not have a persistent uuid,
>> a reasonable/feasible solution without media format modification is fsid
>> in boot/mount life cycle. That's why huge_encode_dev(sb->s_bdev->bd_dev)
>> is used here.  For jfs and reiserfs3, is there any use case for
>> persistent fsid cross boots ?
> 
> I would say yes, this is worthwhile to do, or the fsid can change between
> boots unnecessarily.
> 
If no partitioning happens between boots/mounts, fsid from huge_encode_dev() should be identical.
For non-uuid file systems, IMHO huge_encode_dev() method is acceptable.
But YES, for jfs and reiserfs3 there is chance to provide persistent fsid cross boots, here are
examples,
- in fs/jfs/super.c:jfs_statfs(), generate f_fsid by:
	buf->f_fsid.val[0] = crc32_le(0, sbi->uuid, sizeof(sbi->uuid)/2);
	buf->f_fsid.val[1] = crc32_le(0, sbi->uuid + sizeof(sbi->uuid)/2,
					sizeof(sbi->uuid)/2);
- in fs/reiserfs/super.c:reiserfs_statfs(), generate f_fsid by:
	buf->f_fsid.val[0] = (u32)crc32_le(0, rs->s_uuid, sizeof(rs->s_uuid)/2);
	buf->f_fsid.val[1] = (u32)crc32_le(0, rs->s_uuid + sizeof(rs->s_uuid)/2,
				sizeof(rs->s_uuid)/2);

I will update corresponded patches for the implementation. Thanks for your comments.

-- 
Coly Li
SuSE Labs
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